MXenes are a recently discovered family of two-dimensional transition metal carbides, nitrides, and carbonitrides with electronic properties that can be tuned by their chemistry and structure. Herein THz spectroscopy was used to investigate the microscopic conductivity and photoexcited charge carrier dynamics in two Mo-based MXenes: Mo₂Ti₂C₃T_z and Mo₂TiC₂T_z. We find that both have high intrinsic carrier densities (∼10²⁰ cm^–3 in Mo₂Ti₂C₃T_z and ∼10¹⁹ cm^–3 in Mo₂TiC₂T_z) and mobilities and exhibit high conductivities within individual nanosheets. Optical excitations result in a transient conductivity increase in both compositions, in stark contrast with the most studied member of the MXene family, Ti₃C₂T_z, where photoexcitation suppresses the conductivity for nanoseconds. Deintercalation of water, and other species, from between the nanosheets by mild vacuum annealing at 200 °C further improves the long-range, internanosheet transport of the photoexcited carriers and increases their lifetime. High, and long-lived, photoinduced conductivity that can be engineered by substituting Mo for Ti renders these Mo-based MXenes attractive for a variety of optoelectronic, sensing, and photoelectrochemical applications.

中文翻译：

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二维MXenes Mo ₂ Ti ₂ C ₃ T _z和Mo ₂ TiC ₂ T _z：光激发载流子的微观电导率和动力学

MXene是最近发现的具有电子性质的二维过渡金属碳化物，氮化物和碳氮化物家族，可以通过其化学性质和结构进行调整。本文使用太赫兹光谱研究了两种基于Mo的MXene：Mo ₂ Ti ₂ C ₃ T _z和Mo ₂ TiC ₂ T _z的微观电导率和光激发电荷载流子动力学。我们发现两者都具有很高的固有载流子密度（Mo ₂ Ti ₂ C ₃ T _z中约为^{10 20} cm ^–3，而约为10 ¹⁹ cm ^–3Mo ₂ TiC ₂ T _z）和迁移率，并在单个纳米片中显示出高电导率。光学激发导致两种成分的瞬态电导率增加，这与MXene系列研究最多的Ti ₃ C ₂ T _z形成鲜明对比。，其中光激发抑制电导率达纳秒。通过在200°C下进行温和的真空退火处理，可将水和其他物种从纳米片之间脱嵌，从而进一步改善了光激发载体的远距离，中间片传输并延长了它们的寿命。可以通过用Mo代替Ti来设计的高且长寿命的光诱导电导率，使这些基于Mo的MXene具有广泛的光电，传感和光电化学应用吸引力。